Method of treating malleable cast iron and product thereof



Sept. 15. 1925. 1,553,907

L. H. MARSHALL IETHOD OI" TREATING HALLEABLE CAST IRON AND PRODUCTTHEREOF Filed April 21. 19231 2 11/2 TEMPERATURE FAHRENHE/T Q Q Q Q O Dt Q a V N Patented Sept. 15, 1925.

UNITED STATES PATENT" OFFICE.

mm H. MARSHALL, 0F MANBI'ELD, OHIO, ASSIGNOR TO THE OHIO BRASS COI-PANY, OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY.

moo or memo mmmm our men Ann rnonuc'n 'rr.

Application filed April :1, 1923. Serial No. 838,789.

To all. whom it ma concern:

' Be it known that Lnsnm H. MARSHA-LL a citizen of the United States ofAmerica, residing at Mansfield, in the county of Richland and State ofOhio, have invented certain new and useful Im rovements in Methods ofTreating Mallea 1e Cast Iron and Products Thereof, of which the followinis a specification.

%his invention relates to metallurgy. More specifically it relates to aprocess of treating malleable cast iron and to the product of thatprocess.

One of the objects of the invention is to provide a rocess of treatingmalleable cast iron whereby certain new and valuable properties areimparted thereto.

Another object is to provide malleable cast iron having new and valuableproperties and characteristics.

Other objects are to provide a process of galvanizing, sherardizing, orotherwise coating malleable iron without impairing the properties of theiron and to provide malleable cast iron so coated and having certain newproperties and characteristics. Still further objects will appear as theinvention is hereinafter disclosed.

For many years it has been found that hot galvanizing, sherardizing, orsimilarly treating malleable cast iron renders a comparat-ively largeportion of a heat, brittle, less ductile, crystalline in fracture andlow in resistance to shock, while the remainder of the same heatpossesses its properties and characteristics substantially unimpaired.In the heretofore unsuccessful efforts to solve the problem ofgalvanizing, sherardizing or' similarly coating, malleable cast iron tosecure a uniform product of substantially unimpaired characteristics andproperties, many different theories have been advanced among which arethe following: that the composition of the hard iron beforemalleableizing affects the ultimate product, that the treatment oftheiron in the annealing or malleableizing process enters into the problem,that the process of pickling or cleaning the castings, the temperatureof the zinc bath, the temperature of the quenching bath, the rate ofcooling after coating, the dissolving action of the are the following: t

molten zinc, or combinations of these and other steps enter, into theproblem.

I have discovered that as the temperature of normal malleable cast ironis raised it passes successively through the following ranges or zonesof temperature:

(a) A danger zone, 1. e., a range of temperature such that if the ironis raised to a temperature within that zone and subseuently cooled, theiron often, though not invariably, becomes brittle and otherwise changesits properties.

(6). A neutral point, i. e. a tem erature at which the iron, when raisedto t at temperature and then cooled, possesses substantially the samedegree of malleability or dresilience as it possessed before heating, an

(c) A safety zone, i. e., a range of temperature such that if the. ironis raised to a temperature within that zone and subsequently cooled, themalleability and other desirable properties of the iron will bemaintained or improved.

My heat treating process differs from the annealing or re-annealingprocesses of the PIIOI art in various respectsamongwhich When the socalled hard iron is anneale erties therein or the annealed ironreannealed, it is brought to a temperature above that of thecarbon-combining or critical temperature of that particular iron,maintained at that temperature for a period depending upon .thecomposition of the iron and the temperature to which it has been raised,and subsequently cooled. In my process of treating malleableized iron,the temperature of the iron is not raised above the carbon-combining orcritical temperature, but its maximum temperature is kept below thecritical temperature. Again, malleable cast iron which has been annealedor re-annealed, in accordance with the processes of the prior art, isnot stable but when subsequently raised to a temperature within 'thedanger zone (as in case of hot galvanizing or similarly coating) isbeyond control of the operator in that hehas no assurance that theironwill not become embrittled, and large quantities of malleable ironcastings commonly become embrittled whereas others 0 produce malleableprop-- are reliable, though the composition and annealing process areapparently the same in either case. On the other hand, the product of myprocess is stable, i. e., it uniformly retains its malleability evenwhen subsequently heated to a temperature within the 'danger zone as inhot galvanizing or similar- 1y coating the iron.

specimens from 392 F. to a corresponding one of a number of differenttemperatures between 392 F. and 1472 F., held each particular specimenat its higher temperature for three minutes and then quenched in waterat 175 F. After quenching, each specimen was tested in an impact machineof the Izod type to determine its resiliency. Such use of an Izodmachine is known to those skilled in the art. It consists in measuringthe footpounds required to fracture a notched s ecimen (notching isstandard practice) un or test. As to each specimen, I plotted thetemperature to which it had been raised as the abscissa and thepercentage impact value of that specimen, as determined from the Izodtest machine, as the corresponding ordinate. Therefore, the ordinate ofeach point on the curve A represents to scale, on a basis of 100 as theimpact value of normal malleable cast iron before heating, thepercentage impactvalue of a particular one of a number of specimens, alltaken from the same piece of commercial malleable cast iron, and whichparticular specimen has been raised to a temperature indicated by thecorresponding abscissa, and then subsequently treated by quenching asabove described.

It will be observed that as the treating temperature is increased from392 F. to substantially 700 F. the resulting malleable cast iron showsincreasing embrittlement to a point where the resistance to breaking isonly about 16% of that of the untreated product. From 700 F. to 1020 F.the effect of increasing the temperature does not appear to furtherincrease the em- 'brittlement, but at approximately 1020 F.

the curve suddenly rlses, crossing the 100% line which I have termed thenormal line, at a temperature of 1103 F.', and reachin a point where ata temperature of 1130 the resistance under impact to breaking is productwill withstand a 54% greater impact blow than the untreatedproduct'before it will break and is therefore more resilient. Byincreasing the temperature above 1130 F. and up to substantially 1400 F.(the critical temperature at which the free carbon in this iron beginsto recombine) the resistance to impact is lowered slightly from that at1130 F and the curve further shows by its sudden drop that a heattreatment above 1400 F. will cause a decrease in the resiliency as shownby the decrease in the impact value.

The malleable cast iron upon which the tests shown by curve A in Fig. 1are based, contained Total carbon Q. 2.10 Silicon .80 Phosphorus 2O Mananese .26 Sulp ur 073% Inspection of curve A will indicate that thedanger zone of the articular malleable cast iron there raphically shownlies below 1103 F. and t at the safety zone thereof lies between 1103 F.and 1400 F; The neutral point or temperature marks the dividing pointbetween the danger and safety zones and this neutral point is indicatedby the intersection of the curve with the 100% line, the abscissa of theintersection being 1103 F.. It will be noted that the curve A is quitesteep at its intersection with the 100% line and rises rapidly to a peakat about 1130 F. In other words, if the particular iron is raised to atem erature of about 1103 F. and then quenc ed its impact value will bethe same as when untreated but when raised to a temperature of about1130 F. and then quenched the impact value is increased substantially54%. In view of these facts and the difliculty of close temperaturecontrol or regulation, it is preferable to raise the temperature of theiron to at least 1130 F., and beter still 1200 F., and then quenchsilicon, plhosphorus .15%, manganese .31%

and sul ur .08%. The specimens were subjected to the same treatment asthe specimens and to secure I covered by curve A. Curve-.B difi'ers fromcurve A as would be expected on account of the difference in thechemicalcomposition, but here too we find a zone of heat treatment which willproduce embrittlement and a zone of heat treatment which will improvethe resiliency or impact value of the iron over and above that of theuntreated iron. The iron represented b' curve B shows that it is notne'cessal to eat it to the temperature required by te iron representedby curve A and the increase in impact value is not as great, neither isthe .embrittlement as great when heated within the danger zone. Thisiron is not as sensitive to a temperature below the neutral point anddoes not respond in as great a degree in increased resiliency with theheat treatment, as the iron covered by curve A, but still curve B showsthat, as in the case of curve A, there is a distinct embrittlement zone,and a distinct temperature zone within which the iron can be treated andimproved.

I have further found that normal or commercial malleable cast ironhaving a composition of total carbon 2.35%, silicon .91%, phosphorus.18%, manganese 25% and sulphur .051% when heat treated to a temperatureof approximately 1200 F. and then quenched in water at 175 F that theimpact value as measured by the Izod type of impact machine was 148% ofthe impact value of the same malleable cast iron untreated or 48%greater.

Tests thus far made by me indicate that the time rate of temperatureincrease in bringing the iron 11 to the treatment temperature is ofrelatively minor importance.

Limited tests made to date seem to indicate that the rate ofcooling fromthe heat treatment temperature has some effect upon the impact value orresiliency of the heat treated iron, in that quenching in the air tendsto give a product of a higher impact value than quenching in hot Wateror oil and when allowed to cool with the heating furnace an even higherimpact value is secured as shown by the following table which shows theresults secured upon the same malleable cast iron used in the testsrepresented by the curve A in Fig. 1.

Time at 1255 F. Method of quenching. f

Per cent 3 minutes Cooled with furnace 18 3minutes. In air 140 3 minutesIn hot water 175 F 1313 Same iron untreated 100 observations of thesameiron as was tested to obtain the-immediately preceding table.

' 1111 t Time at law F. Quenched. v

' Per cent. 300 minutes In water-175 F. 1% 50 minutes In water-175 F..166 3 minutes In water-175 F 133 Same iron untreated I00 Bearing in mindthat hot galvanizing of malleable cast iron is accomplished in a zincout by experience in the practical art of hot galvanizing malleable ironcastings.

A further and very important feature of my discover and inventionresides in the fact that a ter malleableized cast iron is heated tocause its temperature to pass through and beyond the danger zone andinto the safety zone and then further treated as above described byquenching, it retains the resiliency or impact value and other desirablecharacteristics and properties imparted to it by such treatment evenwhen subsequently heated to carry it into the danger zone and on thedanger zone side of the neutral point or temperature. Thus I found,after treating specimens of malleable cast iron as set forth inconnection with curves A and B (including the step of elevating thetemperature of the iron into the safety zone) and subsequently reheatingthe iron to 844 and quenching-in water at l'(' .5 F., that the reheatingafter the heat treatment did not decrease the impact value. In otherwords the benefits secured by the heat treatment at 1200 F., or othertemperature within the safety zone including the steps of quenching,remain fixed. In fact, after heat treatment to 1200 F. and subsequentreheating to 844 F., malleable cast iron showing an impact value of 160%of the untreated iron has been produced by me. The same heat treatmentand reheating just described, when carried out on normal malleable cast1 iron having a carbon content of 2.10% and a silicon content of 0.80%showed an impactvalue of 139% of the impact value of specimens beforetreatment in accordance with my rocess.

I ave also found that my process is not only effective in preventing theembrittlement of commercial malleable cast iron, but that the ironrepresented in curve A if it has become embrittled, as by hotgalvanizing, sherardizing, etc, may be reclaimed by .heat treating suchembrittled product be- 7 again hot, galvanized, sherardized, etc.,without cndangering'its malleable properties.

Reeapitulatingin accordance with my invention, I have provided a processof treating normal malleable cast iron whereby it malleability and otherdesirable properties possessed by it prior to treatment are maintained,or preferably increased, and retained even though subsequently heated toa temperature within and not beyond the danger-zone; a novel product, i.e., malle .able cast iron having high resilience and other desirablecharacteristics and properties and which are retained though the iron beheated to a temperature within and not betreatmg malleable cast ironwhic 0110 01 more yond the danger zone; a process of hot galvanizing orsimilarly coating malleable cast iron without impairing, but ifdesirable increasing, its resilience and other desirable properties,novel galvanized or similarly coated malleable cast iron products; and aprocess for reclaiming malleable cast iron which has been embrittled byhot galvanizing or otherwise coating it in accordance with the processesof the prior'a-rt. It is my present intention to direct the claims ofthe present application to the rocess of as above described includes thesteps of heating the iron to a temperature within the safet zone,maintaining it at such temperature or the desired length of time, andthen cooling the iron by quenching; and to claim the other features ofinvention, herein disclosed, in

divisional or continning'applications.

The embrittlement is shown, by my investigations, to be overcome whennormal malleable cast iron is subjected to the process herein disclosed,and actual practice in the application of my, process has proved con- 0usively that my process is'practical and can be applied withoutexpensive equipment,

and where the loss due to hotgalvani zing, embrittling the iron has beenvery large and uncontrollable, such loss will be practically eIiminatedby my invention. 4

The process described can be carried out by placing the commercialmalleable cast iron castings to be heat treated in a furnace having asource of heat to bring them up to the temperature required preferablywithin the safety zone, and allowing them to remain at the desiredtemperature for a period .of

I have. found that my process is ap licable' to malleable cast iron ofvarying c emical composition, and which has been put through therecognized commercial annealing treatment in the malleableizing process.In this case, the novel treatment may be applied to the iron byquenching it after its temperature has been brought below the criticalor carbon-combiningtemperature and before its temperature has droppedbelowv the safety zone of temperature described above.

In view of the variable conditions met with in commercial malleable castiron I do not wish to be limited strictly to any specific temperature,time, rate of cooling or other conditions, as different grades orcompositions ofiron may change the temperature treatments required, asalready shown by curves A and B, and some grades of iron may requiredifferent times under the treatment temperature and different rates andmeans'of coolin nor do I wish to be limited to the composition of themalleable cast iron to which my invention is applicable. I have found,however, that there is a definite range of temperature, for a givengrade of malleable cast iron, between the limits of which the' iron isembrittled and another range, between the limits of which the iron isimproved (see Fig. 1) and rendered immune from emb'rittlement when againheated at a lower tem nature as in galvanizing.

I find -t at treating at a temperature of approximately 1200 F., andthen quenching will as a rule secure the desired results, as thistemperature falls safely within the heat treatment or safet zone of mostgrades of commercial mallea le cast iron.

From the. curves shown in Fig. 1 it will be apparent to one skilled inthe art that since there are two well defined zones as described, andthat heating normalmalleable cast iron to a temperature within the zonewhich I haves cified, as the safety zone and then quenc ing will protectthe iron from 'embrittlement when reheated to a temperature fallingwithin the danger zone, that one who is producing-malleable cast iron oron'e'who is using malleable cast iron can stabilize or protect the sameagainst embrittlement b subjecting the iron to a series of tests atifi'erenttem eratures to determine exactly. the limits of t e safety anddanr zones, or by determinin the limits of the safety? zone of theparticu ar iron and heat treati the iron according to the resultsdetermined and the method I have disclosed.

To hot galvanize malleable cast iron castings I first subject them to atemperature within the range of the heat treating or safe ty zone asdescribed and then cool or quench In the appended claims I use the wordquenched, orquenching, to indicate air cooling; or liquid cooling; orcoolin in a furnace but at a comparatively rapi rate such,

for example, as would take place in a comparatively small or ex rimentalfurnace as distinguished from a arge commercial fur-- nace.

What I claim is 1. The process of treating malleableized cast ironcomprising heating the iron in a continuous furnace to a temperaturewithin the safety zone, and then quenchin the iron.

2. The process of treating mal eableized cast iron consisting in heatingthe iron to approximately 1200 F., and then quenching.

3. The process of treating malleableized cast iron comprising placingthe iron in a furnace and bringin the iron to a tem erature ofapproximate y 1200 F., and ho ding the iron at this temperature and thenquenching the iron to immunize the iron against da r of embrittlementwhen reheated below 1ts neutral temperature.

4. The process of treating malleableized cast iron comprising heating 1tto a temperature not to exceed its critical tem erature and thenquenching, whereby t e iron is rendered immune from embrittlementwhen/if later heated below its neutral temperature.

5. The process of treating malleableized cast iron comprising heatin theiron to a temperature not to exceed its critical temperature and wherebyit is rendered immune from embrittlement when/if later heated below theneutral temperature.

6. The method of treating malleableized cast iron which comprisesheating the iron to cause its temperature to rise through the zone oftemperature at which the iron is in danger of embrittlement, and coolingthe iron before the carbon-combining temperature is reached.

7. The process of treating malleableized cast iron comprising heatingthe iron to a temperature not to ex substantially 1400 F. and not belowa temperature which will tend to decrease the impact value of the ironbelow that of the untreated iron. 7

8. The process of treating malleableized cast iron consisting in heatingthe iron to a temperature not to exceed substantially 1400 F. and notbelow a temperature which will tend to decrease the impact value of theiron below thatof the untreated iron and then quenching the iron.

9. Themethod of'treating malleableized cast iron which has athermal zonebetween the limits of which the iron is embrittled if heated and anotherthermal zone between the limits of which the iron is rendered immunefrom embrittlement if heated, said method comprising heating said ironto a temperature falling within the limits of said latter zone.

10. The method of treating malleableized cast. iron which has a thermalzone between the limits of which the iron is embrittled if heated and athermal zone between the limits of which, the. resiliency of the iron isincreased over and above that of the untreated iron, said methodcomprising heating the iron to a temperature falling within the limitsof said latter zone, and then quenching the iron.

11. The method of treating malleableized cast iron which has a thermalzone between the limits of which the iron is embrittled if heated andanother'thermal zone between the limits of which the iron is renderedimmune from embrittlement if heated, said method consisting in heatingsaid iron to a temperature falling within the limits of said latter zoneand then quenching the iron.

12. The method of producing malleable cast iron comprising the steps ofannealing the iron in the hard iron condition to change-thecombined'carbon into free or graphite car-. bon, then stabilizing theannealed iron by heating it to a temperature in excess of that whichwill cause the iron to be embrittled, and then quenching the iron.

13. The method of heat treating malleable cast iron comprising firstsubjecting a plurality of like samples of the iron each to a differenttemperature between room temperature and its critical temperature for auniform period of time, then uniformly cooling, and then subjecting eachsample to a mechanical test which will measure its resiliency, thencomparing the results with a like test upon a like sample untreated andthen subjecting the iron to be treated to a temperature in excess ofthat which it is found by the samples treated to give a greater degreeof resiliency than the untreated sample.

14. The method of'reclaiming malleable cast iron which has beenembrittled byheating to below the neutral temperature, comprisingheating the iron to a temperature iron at that temperature for a betweenthe neutral temperature and the critical temperature.

15. The method of reclaiming malleable cast iron which has beenembrittled by heating to a temperature below the neutral temperature,comprising heating the iron to such temperature below the crit caltemperature as will remove said embrittlement.

16. The method of heat treatingv malleableized cast iron comprisingsubjecting the iron to a temperature in'excess of its neutraltemperature and below its critical temperature.

17. The method of producing malleable cast iron comprising the step ofheating the iron to a temperature above the carboncombining temperature,maintaining the eriod dependent upon the composition 0 the iron and thetemperature to which it has been raised, and cooling the iron to atemperature below the carbon-combining temperature, in accordance withthe ordinar American commercial annealing operation; and then quenchinthe iron while its temperature is above the neutral temperature.

18. The method of improving the physical properties of malleableizedcast iron comprising heat treating the iron to a temperature fallingwithin the safety zone described, and then quenching the iron,

19. The method of treating malleableized cast iron comprising in firstsubjecting the iron to a test to determine the neutral temperature andthen heating to a temperature above the neutral temperature and belowthe critical temperature. a

20. The method of stabilizing the malleability of malleableized castiron which comprises heating the iron to cause its. temperature to passthrough the zone of tem erature at which the iron is in danger obecoming embrittled, and cooling the iron before the carbon-combingtemperature has been reached.

21. The process of improving physical properties of normal malleableizedcast iron consisting in heat treating the iron to a temperature withinthe saftey zone and then quenching.

22. The method of producing malleable cast iron comprising the steps ofheating the iron to a' temperature above the carbon-combiningtemperature, bringing the iron to a temperature belowthecarbon-combining temperature, and then quenching the iron while itstemperature is above that which will cause the iron to be in danger of'embrittlement.

23. The method of producing malleable cast iron comprising the steps ofheatin the iron to a temperature above the caliom combining temperature,bringing the iron to a temperature below the carbon-combiningtemperature, and then quenching the iron in liquid while its temperatureis above that which will cause the iron to be in danger ofembrittlement.

In testimony whereof I aflix my signature.

LESLIE H. MARSHALL.

